A group III nitride-based compound semiconductor typified by gallium nitride (GaN), that is, a so-called nitride semiconductor has attracted attention as a material for new devices such as a light emitting diode (LED), a laser diode (LD) and a power device. The nitride semiconductor is a compound semiconductor formed of indium (In), gallium (Ga), and aluminum (Al), which are group III elements, and of nitrogen (N) which is a group V element. A general formula of the compound semiconductors is represented by InxGayAl1-x-y-zN (0≤x≤1, 0≤y≤1, x+y≤1).
Although heterogeneous substrates such as sapphire or Si are commonly used as a substrate for forming a group III nitride semiconductor device, a group III nitride semiconductor thin film formed on these substrates has a high dislocation density and cannot exhibit the original physical potential of the nitride semiconductor. Although a GaN substrate, which has a lower dislocation density than that of the heterogeneous substrate, has been commercialized, the dislocation density and the variation in crystal orientation of the substrate are still large. In addition, the GaN substrate is expensive.
Currently, a nitride-based LED mainly uses a sapphire substrate or a GaN substrate as an under-substrate. Since a Si substrate does not allow the transmission of an emission wavelength of the LED, the Si substrate is hardly used for LED applications. In the case of the sapphire substrate that is the most commonly used, since the substrate is insulative and the thermal conductivity thereof is not high, it is common to adopt a flip-chip structure in which a p-side ohmic electrode and an n-side ohmic electrode are formed on one side surface (for example, see Japanese Patent No. 4118370 (Patent Document 1)).
However, there is also a problem in a flip-chip light emitting diode element having a configuration in the related art. In this type of light emitting diode element, when the light-emitting diode element is operated, an operating current flows through an n-GaN layer in a lateral direction (representing a direction orthogonal to a stacking direction of the layers as applied below). Therefore, in this type of light emitting diode element, a relatively large series resistance (hereinafter, also referred to as “lateral resistance”) based on the resistivity of the n-GaN layer is added when the operating current flows through. As a result, an operating voltage may be increased.
The present disclosure is made to solve the above problems, and an object thereof is to provide a flip-chip light emitting diode element capable of reducing lateral resistance and a method for manufacturing the light emitting diode element.